Fish knife



FIG. 1 is a perspective view of my fish knife embodying my new design;

FIG. 2 is a plan view;

FIG. 3 is a right elevation view;

FIG. 4 is a bottom view;

FIG. 5 is a left elevation view;

FIG. 6 is a rear view; and,

FIG. 7 is a front view. 

The ornamental design for a fish knife, as shown and described. 